Finite Element Model Predictions Research Articles

Predicting the impact of water transport on carbonation-induced corrosion in variably saturated reinforced concrete

A modelling framework for predicting carbonation-induced corrosion in reinforced concrete is presented. The framework constituents include a new model for water transport in cracked concrete, a link between corrosion current density and water saturation, and a theory for characterising concrete carbonation. The theoretical framework is numerically implemented using the finite element method and model predictions are extensively benchmarked against experimental data. The results show that the model is capable of accurately predicting carbonation progress, as well as wetting and drying of cracked and uncracked concrete, revealing a very good agreement with independent experiments from a set of consistent parameters. In addition, insight is gained into the evolution of carbonation penetration and corrosion current density under periodic wetting and drying conditions. Among others, we find that cyclic wetting periods significantly speed up the carbonation progress and that the induced corrosion current density is very sensitive to concrete saturation.

Mechanistic Study of Failure in CFRP Hybrid Bonded-Bolted Interference Connection Structures under Tensile Loading.

Hybrid bonded-bolted composite material interference connections significantly enhance the collaborative load-bearing capabilities of the adhesive layer and bolts, thus improving structural load-carrying capacity and fatigue life. So, these connections offer significant developmental potential and application prospects in aircraft structural assembly. However, interference causes damage to the adhesive layer and composite laminate around the holes, leading to issues with interface damage. In this study, we employed experimental and finite element methods. Initially, different interference-fit sizes were selected for bolt insertion to analyze the damage mechanism of the adhesive layer during interference-fit bolt installation. Subsequently, a finite element tensile model considering damage to the adhesive layer and composite laminate around the holes post-insertion was established. This study aimed to investigate damage in composite bonded-bolted hybrid joints, explore load-carrying rules and failure modes, and reveal the mechanisms of interference effects on structural damage and failure. The research results indicate that the finite element prediction model considering initial damage around the holes is more effective. As the interference-fit size increases, damage to the adhesive layer transitions from surface debonding to local cracking, while damage to the composite matrix shifts from slight compression failure to severe delamination and fiber-bending fracturing. The structural strength shows a trend of initially increasing and then decreasing, with the maximum strength observed at an interference-fit size of 1.1%.

RC beams flexurally strengthened with CFRP sheets combined with FRC layer for mitigating debonding failures

A hybrid strengthening system, comprising a carbon fiber reinforced polymer (CFRP) sheet combined with fiber reinforced concrete (FRC) layer is proposed in this study as a mitigatory solution to brittle debonding problems. Five reinforced concrete (RC) beams, comprising both control cases and those strengthened with the hybrid CFRP-FRC system at various FRP reinforcement ratios, were fabricated and tested to assess the system's effectiveness. A comprehensive finite element (FE) model was also developed to complement the experimental campaign and extend it into a parametric investigation on the effects of FRP reinforcement ratio (ρf), fiber percentage in FRC (vf), and FRC layer thickness (tFRC). Compared with beams strengthened with FRP alone, using the FRC layer increased the ultimate load (Pult.) of FRP-strengthened beams by 29–59%, depending on ρf and vf. The ductility of the hybrid FRP-FRC strengthened beams also increased by more than twice compared to the beams strengthened with only FRP. For the FRP reinforcement ratio (ρf) of 0.18%, use of an FRC layer with vf = 2% yields the highest increase in Pult. and ductility for the hybrid system. Ultimately, the brittle FRP debonding failure was successfully eliminated using the FRC layer, leading to desirable FRP rupture. Built with capabilities to capture material nonlinearity, contact, and debonding phenomena, the FE model predictions excellently matched those of the test results in terms of the beam’s capacity, failure modes as well as load-deflection and load-strain responses.

Verification and Validation of finite element models for laminated timber structures using solid, solid-beam and solid-shell approaches

Verification and Validation of finite element models for laminated timber structures using solid, solid-beam and solid-shell approaches

Nanofabricated high turn-density spiral coils for on-chip electromagneto-optical conversion

Circuit-integrated electromagnets are fundamental building blocks for on-chip signal transduction, modulation, and tunability, with specific applications in environmental and biomedical micromagnetometry. A primary challenge for improving performance is pushing quality limitations while minimizing size and fabrication complexity and retaining spatial capabilities. Recent efforts have exploited highly involved three-dimensional synthesis, advanced insulation, and exotic material compositions. Here, we present a rapid nanofabrication process that employs electron beam dose control for high-turn-density diamond-embedded flat spiral coils; these coils achieve efficient on-chip electromagnetic-to-optical signal conversion. Our fabrication process relies on fast 12.3 s direct writing on standard poly(methyl methacrylate) as a basis for the metal lift-off process. Prototypes with 70 micrometer overall diameters and 49–470 nm interturn spacings with corresponding inductances of 12.3–12.8 nH are developed. We utilize optical micromagnetometry to demonstrate that magnetic field generation at the center of the structure effectively correlates with finite element modeling predictions. Further designs based on our process can be integrated with photolithography to broadly enable optical magnetic sensing and spin-based computation.

Unreinforced masonry walls under two-way out-of-plane bending: Comparison of FE model predictions with analytical models

Four existing design guidelines based on the virtual work method have been compared to predict the out-of-plane (OOP) bending capacities of unreinforced masonry (URM) walls to one-way and two-way actions. The two-way OOP bending design equation as per the Australian masonry standard (AS 3700) and the three subsequent models developed by other researchers are based on specific wall geometries, support conditions, dimensions and strengths of masonry units and mortar. Due to limited experimental data available on URM walls under two-way bending, it is difficult to carry out a detailed investigation of the performance of these two-way design models against all the design parameters. This paper applies the finite element (FE) modelling technique to generate data and extensively investigate the influence of support conditions, pre-compression and aspect ratio on the two-way OOP bending capacity of URM walls. An explicit FE model previously developed by the authors where masonry is macroscopically modelled as an anisotropic composite material, is used for this purpose. Performances of three key parameters (i.e., moment capacity under horizontal bending and diagonal bending and torsional shear strength of masonry) that differentiate the four design models are investigated against varying levels of vertical pre-compression and flexural tensile strength of masonry. The OOP bending capacity predicted by the FE model is compared with the predictions of the design models. Results show that three out of four design models generally overpredict the two-way OOP bending capacities of square and taller walls. Further refinement to the AS 3700 design equation has been proposed in a modified model. The outcomes of this research will help to improve the design of masonry walls under OOP bending.

Pull-out resistance of connected K-wires for osteosynthesis: development of a numerical model

A predictive finite element model was developed to investigate the best configuration of a fixation pins system consisting of two K-wires inserted in a synthetic model (Sawbones®) at different angles and secured to a connecting rod. Two key parameters were considered to determine the best configuration delivering the higher pull-out strength and lower pull-out length: the diameter and insertion angle. Results show that as the diameter and insertion angle increased, the pull-out force increased, while the pull-out length decreased. Results are successfully compared with available experimental data in literature. This model can be used as an alternative to experimental study.

3D-DXA Based Finite Element Modelling for Femur Strength Prediction: Evaluation Against QCT.

Osteoporosis is characterised by the loss of bone density resulting in an increased risk of fragility fractures. The clinical gold standard for diagnosing osteoporosis is based on the areal bone mineral density (aBMD) used as a surrogate for bone strength, in combination with clinical risk factors. Finite element (FE) analyses based on quantitative computed tomography (QCT) have been shown to estimate bone strength better than aBMD. However, their application in the osteoporosis clinics is limited due to exposure of patients to increased X-rays radiation dose. Statistical modelling methods (3D-DXA) enabling the estimation of 3D femur shape and volumetric bone density from dual energy X-ray absorptiometry (DXA) scan have been shown to improve osteoporosis management. The current study used 3D-DXA based FE analyses to estimate femur strength from the routine clinical DXA scans and compared its results against 151 QCT based FE analyses, in a clinical cohort of 157 subjects. The linear regression between the femur strength predicted by QCT-FE and 3D-DXA-FE models correlated highly (coefficient of determination R2 = 0.86) with a root mean square error (RMSE) of 397 N. In conclusion, the current study presented a 3D-DXA-FE modelling tool providing accurate femur strength estimates noninvasively, compared to QCT-FE models.

Numerical analysis and optimization of CFRP buckle arrestors in subsea pipelines

This research investigates the collapse mechanisms and crossover pressure capacity of carbon fiber-reinforced polymer (CFRP) buckle arrestors in subsea pipelines. A nonlinear three-dimensional finite element (FE) model was formulated using ANSYS framework, incorporating a nonlinear geometric algorithm to simulate the collapse and crossover failures. The study underscored a good agreement between the FE model predictions, experimental observations done by the author, and previous research outcomes. Two principal crossover modes; flattening and U-shape modes were identified, though initiated similarly, differ in progression, attributed to the arrestor's attributes. The arrestor thickness ratio (h/t) emerged as a significant determinant of arresting efficiency, particularly impactful when h/t ≥ 1.5. An inverse relationship between σyp/σuc and PX/PP was identified. Furthermore, specific geometric parameters, like h/t and L/D, delineate the predominant crossover mode. Finally, new empirical expressions including the geometric and material parameters are proposed to predict the crossover pressure (PX) for each crossover mode, separately. Also, the findings suggest that CFRP arrestors, especially those with configurations of L = 1.5D and h = 3t, can offer optimum resilience to external pressure.

Piezoelectric impedance-based high-accuracy damage identification using sparsity conscious multi-objective optimization inverse analysis

Two elements are essential in structural health monitoring utilizing dynamic responses: response measurement with high-frequency contents, i.e., small characteristic wavelengths, that can adequately reflect damage features, and effective inverse identification analysis that is however oftentimes under-determined. The advancement of smart structure integration has led to active interrogation through frequency-sweeping piezoelectric impedance measurement at high frequency range. In this research we develop a multi-objective optimization formulation for the identification of damage location and severity utilizing piezoelectric impedance. While one optimization objective is to match the response measurement with finite element model prediction in the damage parametric space, the other is the number of locations of damage, i.e., the sparsity of damage index as the solution vector, since damage usually occurs within a small number of locations. This multi-objective formulation fits well the under-determined nature of damage identification, as it naturally provides multiple solutions as basis for further elucidation. The challenge remaining is how to find a small solution set that can include the actual damage scenario. Here we develop a novel inverse identification framework utilizing the intelligent swarm optimizer which possesses flexibility for enhancement. We first embed a sparsity enforcement process into the population generation of the optimizer, which yields a solution repository intrinsically possessing sparsity. We then apply reinforcement learning so the agents can adaptively opt for local strategies with the aim of enriching the searching patterns to diversify the solutions. Through the incorporation of a Q-table, searching toward more promising directions will be rewarded. Our case analyses employing experimental data indicate that this sparsity-conscious multi-objective particle swarm optimization technique can lead to a small solution set which generally encompasses the true damage scenario. This effectively solves the structural damage identification problem with piezoelectric impedance measurement.

Investigation of single and multicell honeycomb reinforced shape memory polymer composites: Shape optimization and experimental characterization

Honeycomb materials as reinforcements for shape memory polymers have been considered for their commercial availability, ease of geometric tailoring, and high in-plane stiffnesses. The design optimization of these honeycomb cells remains an open field of research, with many approaches taken in formulating the structural optimization problems. This investigation focuses on implementing a shape variable parametrization of the honeycomb to study the possible value of both cell asymmetry and spatially varying cell geometries in multicell networks. A unit cell finite element model framework was developed to predict the in-plane elastic properties of these composites, and two design objectives were selected to be optimized. Pareto fronts were estimated for multiple loading cases and cell wall material models, and experimental results were collected for model validation. The optimization results find that these composites can achieve a large range of performances, with maximum moduli as high as 17.2 GPa. Large asymmetry is found in the optimized cell geometries, and relationships are identified between loading cases and for different wall materials. Furthermore, the experimental results validate the finite element model predictions, with relative errors as low as 20% for the predicted maximum modulus and 2% for the modulus ratio.

Verification Process for Finite Element Modeling Techniques Used in Biological Hard Tissue

Abstract An approach is presented for calculation verification of geometry-based and voxel-based finite element modeling techniques used for biological hard tissue. The purpose of this study is to offer a controlled comparison of geometry- and voxel-based finite element modeling in terms of the convergence (i.e., discretization based on mesh size and/or element order), accuracy, and computational speed in modeling biological hard tissues. All of the geometry-based numerical test models have hp-converged at an acceptable mesh seed length of 0.6 mm, while not all voxel-based models exhibited convergence and no voxel models p-converged. Converged geometry-based meshes were found to offer accurate solutions of the deformed model shape and equivalent vertebral stiffness, while voxel-based models were 6.35% ± 0.84% less stiff (p < 0.0001) and deformed 6.79% ± 0.96% more (p < 0.0001). Based on the controlled verification study results, the voxel-based models must be confirmed with local values and validation of quantities of interest to ensure accurate finite element model predictions.

Data-informed statistical finite element analysis of rail buckling

In this paper, the statistical finite element method is developed further to synthesize distributed rail response data with nonlinear finite element model predictions within and outside the measured loading range. In the data-generating model of the statistical finite element method, the distributed sensing data is decomposed into a finite element model component, a model-reality mismatch component, and a noise component. Each component is considered uncertain and is represented as a Gaussian random vector with a corresponding prior density. The finite element prior density is updated using the Bayesian statistical framework in light of the distributed fiber optic sensing data. The calculated posterior density enables one to infer the true structural response. The required finite element prior density is determined by solving a conventional stochastic forward problem using a polynomial chaos expansion of random fields and a non-intrusive pseudo-spectral projection approach. In this paper, a lab test involving a section of a rail (i.e., a beam-column structural member) instrumented with distributed fiber optic sensors and subjected to axial load causing progressive lateral buckling is considered to demonstrate the use of the statistical finite element method to improve rail response prediction. The results show improved prediction of true rail strain in linear and nonlinear regimes compared with a pure finite element model-based prediction.

Improved compressive performance of lattice truss core sandwich composites with modified Kagome topologies: An experimental and numerical study

A finite element model (FEM) using a more realistic three-dimensional geometry of lattice truss core was proposed to simulate the flatwise compression test on lattice truss core sandwich composites (LTCSCs). The goal was to reduce the disparity between experimental results and FEM predictions without inclusion of imperfection, as oppose to similar studies. Besides, two modified Kagome topologies were suggested and fabricated by adding vertical composite struts at specific locations. Based on the experimental results, the modified Kagome topologies exhibited superior specific compressive stiffness and strength over the Kagome topology, by about 100%. In addition, facesheet rotation of Kagome topology was found by the FEM, which considerably affect its compressive performance. Facesheet rotation is caused by the arrangement of composite struts of LTCSC. Compressive response of LTCSC was acceptably predicted by the FEM, though there was quite high error for compressive stiffness and strength. Probable sources of discrepancy between experimental and FEM results were discussed.

Corroboration of coupled musculoskeletal model and finite element predictions with in vivo RSA migration of an uncemented acetabular component.

While finite element (FE) models have been used extensively in orthopedic studies, validation of their outcome metrics has been limited to comparison against ex vivo testing. The aim of this study was to validate FE model predictions of the initial cup mechanical environment against patient-matched in vivo measurements of acetabular cup migration using radiostereometric analysis (RSA). Tailored musculoskeletal and FE models were developed using a combination of three-dimensional(3D) motion capture data and clinical computerized tomography(CT) scans for a cohort of eight individuals who underwent primary total hip replacement and were prospectively enrolled in an RSA study. FE models were developed to calculate the mean modulus of cancellous bone, composite peak micromotion (CPM), composite peak strain (CPS) and percentage area of bone ingrowth. The RSA cup migration at 3 months was used to corroborate the FE output metrics. Qualitatively, all FE-predictedmetrics followed a similar rank order as the in vivo RSA3Dmigration data. The two cases with the lowest predicted CPM (<20 µm), lowest CPS (<0.0041), and high bone modulus (>917 MPa) were confirmed to have the lowest in vivo RSA 3D migration (<0.14 mm). The two cases with the largest predicted CPM (>80 µm), larger CPS (>0.0119) and lowest bone modulus (<472 MPa) were confirmed to have the largest in vivo RSA 3D migration (>0.78 mm). This study enabled the first corroboration between tailored musculoskeletal and FE model predictions with in vivo RSAcup migration. Investigation of additional patient-matched CT, gait, and RSA examinations may allow further development and validation of FE models.

Microstructure Analysis and Finite Element Modelling for Creep Failure Prediction and Fitness-For-Service Assessment of Superheater Tubes

Abstract This study aimed to perform a fitness-for-service assessment and investigate the root cause of failure of Grade 14CrMo3 steel seamless tubes typically used in superheaters in power generation plants. For this purpose, samples were taken from in-service superheater tubes in a 320 MW power plant. Thickness and hardness measurements were taken from the samples, and microstructural analyses were performed using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and X-ray diffraction. The results showed the presence of vanadium (V) and sulfur (S) elements on the tubes' external surface (flue gas facing-side), which is indicative of fuel ash corrosion. The formation of low melting point salts, such as Na2SO4, NaVO3, Na2O, and V2O5 (particularly between 10 and 2 o'clock positions) and degradation of the protective oxide layer led to loss of tube wall thickness. On the steam side of the tubes, the formation of an iron oxide layer (particularly between 12 and 2 o'clock positions) and the presence of water in the steam due to the improper function of the steam drum created an insulated zone leading to the formation of localized hot spots, creep microvoids, and spheroidization of carbides. In addition, a thickness reduction of 18% resulted in a considerable increase in hoop stresses having a detrimental effect on the remaining creep life. To explain the creep damage mechanism and determine the remaining creep life, the Larson–Miller criteria and API 579-1/ASME fitness-for-service-1 guidelines were utilized. The effects of the reduction in wall thickness were considered by performing a three-dimensional finite element analysis. The results showed that a temperature increase of only 50 °C (from 480 °C) could decrease the life of the tubes from 30 years to less than a year.

A biomechanical study of osseointegrated patient-matched additively manufactured implant for treatment of thumb amputees.

Thumb amputations leads to 50 % loss in hand functionality. To date, silicone vacuum prosthesis and autologous transplantation are the most adopted treatment solutions: nevertheless, vacuum prostheses lack in stability and cause skin issue and surgical treatment is not always accepted by patients. Osseointegrated implants were demonstrated to enhance stability, restore osseoperception and increase the time of prosthesis use. Thumb amputations present varying stump sizes: a standard size implant cannot address specificity of each patient, while a patient matched solution can meet surgeon requirements, by geometrical features of implant. The fixture presented in the current paper is the first additively manufactured patient matched osseointegrated implant for the treatment of thumb amputees. The current work aims to verify and validate a predictive finite element model (FEM) for mechanical strength of the presented fixture. FEM was demonstrated to correctly evaluate the mechanical strength of patient matched device. Minimum strength requirements were calculated in different core diameters: FEM were experimentally validated. Safety factor of 1.5 was guaranteed. Finally, considerations on performance of the prototype were carried out by means of insertion tests in Sawbones and axial pull-out force assessment. Cadaver tests to evaluate the entire procedure and production process are ongoing.

A fluoroscopic imaging-guided computational analyses to inform internal tissue loads within fat pad of the diabetic foot during gait

To accurately predict internal tissue loads for early diagnostics of diabetic foot ulcerations, a novel data-driven computational analysis was conducted. A dedicated dual fluoroscopic system was combined with a pressure mat to simultaneously characterize foot motions and soft tissue’s material properties during gait. Finite element (FE) models of the heel pad of a diabetic patient were constructed with 3D trajectories of the calcaneus applied as boundary conditions to simulate gait events. The tensile and compressive stresses occurring in the plantar tissue were computed. Predictions of the layered tissue FE model with anatomically-accurate heel pad structures (i.e., fat and skin) were compared with those of the traditional lumped tissue (i.e., homogeneous) models. The influence of different material properties (patient-specific versus generic) on internal tissue stresses was also investigated. The results showed the peak tensile stresses in the layered tissue model were predominantly found in the skin and distributed towards the circumferential regions of the heel, while peak compressive stresses in the fat tissue-bone interface were up to 51.4% lower than those seen in the lumped models. Performing FE analyses at four different phases of walking revealed that ignorance of layered tissue structures resulted in an unphysiological increase of peak-to-peak value of stress fluctuation in the fat and skin tissue components. Thus, to produce more clinical-relevant predictions, foot FE models are suggested to include layered tissue structures of the plantar tissue for an improved estimation of internal stresses in the diabetic foot in gait.

Experimental and Numerical Study of the Flexural Performance of Spontaneous Combustion Gangue Coarse Aggregate Concrete Laminated Slab

(1) Background: to study the differences in flexural performance and failure characteristics of spontaneous combustion gangue coarse aggregate concrete (SCGAC) laminated slabs and ordinary concrete laminated slabs, comparative flexural performance tests of one ordinary concrete laminated slab and four spontaneous combustion gangue coarse aggregate concrete laminated slabs (SCGACLSs) full-scale specimens were carried out. (2) Methods: The loading method was four-point unidirectional static loading; the failure mode, load–deflection curve, load–reinforcement strain curve, and load–concrete strain curve of each specimen were analyzed. In addition, the load–deflection curve of the five slabs were predicted by ABAQUS. (3) Results: The five laminated slabs showed similar behaviors in terms of failure mode, load–strain curve, load–deflection curve, and deformation and all the properties satisfied the Chinese standard GB50010 (2010). Compared with ordinary concrete laminated slabs, the cracking load of SCGACLS with a precast layer of SCGAC(C30) decreased by 15.2% and the span deflection increased by 28.3% in the ultimate condition; however, when the strength grade of SCGAC of the precast layer was increased to SCGAC(C40), the cracking load increased by 7.8% and the span deflection was similar to that of the ordinary concrete laminated slabs. All specimens conformed to the planar section assumption. In addition, the finite element model (FEM) prediction results showed that the maximum relative errors of load and deflection were &lt;5% and &lt;10%, respectively, indicating that the established FEM had high prediction accuracy. (4) Conclusions: The defects of reduced load-carrying capacity and uncoordinated deformation caused by the different elastic modulus of precast and cast-in-place layer concrete can be compensated by appropriately increasing the strength grade of precast layer concrete of SCGACLSs. The application of SCGACLSs in structures is feasible.

Pullout Capacity of Single and Biwing Anchors in a Soft Clay Deposit: Model Investigation in a Centrifuge and FEM Predictions

One of the ways to install plate anchors in deep seabed is to drop the anchor system from the sea level and allow it to initially embed in the seabed under its own weight. Further dragging would cause the anchor to rotate and embed further into the seabed. There could be difficulties of getting the anchor plate horizontal or mooring line to be perpendicular to the plate where the maximum pullout capacity could be achieved. As part of the investigations, various aspects of the plate performance were examined through centrifuge testing in which the plate orientation and pullout angles were varied. It was presumed that dynamic stability of the anchor (during field installation) can be achieved by having the plate in biwing configuration. Therefore, the performance of the biwing anchors having different spacing between the plates was also examined in the centrifuge testing program and the findings were compared with predictions obtained through finite-element modeling (FEM). Both pullout directions and the plate angles considerably influenced the pullout capacity factors. The comparison between the predicted pullout capacity using FEM and measured pullout capacity for biwing anchors at shallow embedment depths was excellent. However, the FEM-predicted pullout capacity was noticeably lower than the measured ones for deep anchors. Pullout capacity of biwing anchors at shallow embedment depth increased as the spacing between the plates S increased from 0 to 0.5B. However, there appears to be a slight reduction in the performance in deep embedment anchors. This is also reflected in FEM findings.